Event triggering of electronic devices is useful in a number of different applications. Examples of event triggered or event driven devices include, but are not limited to, cameras (film or digital), video cameras, and tape recorders. As used herein, the term ‘event triggering’ is defined as ‘causing a device to perform a given operation, action, task, or function in response to the occurrence of an event, the event generally being representative of a state or condition of an environment external to the device’. Examples of external environmental states that are used as event triggers include, but are not limited to, temperature, wind speed, vibration, motion, and illumination intensity. Often, the external state is monitored using a sensor. The sensor monitors the external state (e.g. temperature, vibration, wind speed, etc.) and communicates the condition to the device using a signal parameter such as voltage. The sensor is interfaced to the event triggered device using a dedicated trigger source interface port. To explore the concept of event triggered devices a bit further, consider a digital camera.
Digital cameras that record images in a digital representation are rapidly gaining on conventional photographic film based cameras in both popularity and performance. In particular, the performance of digital cameras in terms of image quality/resolution, image recording speed, and ability to capture images in variable lighting condition has made dramatic improvements in the last decade. At the same time, improvements in memory technology for storing and transporting digital images along with advances in color image printing technologies have complemented the improvements in digital cameras. Moreover, the cost of digital cameras, memory and color image printers are decreasing rapidly. The combination of improved performance and reduced costs has resulted in the application of digital cameras to a wide variety of tasks including those tasks employing event triggering.
For example, a digital camera may be used to record an image of an integrated circuit or other article of manufacture undergoing temperature testing. The camera can record images at one or more specific temperatures. A temperature sensor monitors the temperature and produces a voltage that corresponds to the monitored temperature. An image is recorded when a specific, predetermined temperature is detected by the temperature sensor or equivalently when a specific predetermined voltage is detected by the camera at the trigger source interface port. In another application, a motion detector can monitor an area for the presence of an individual. When an individual enters the area, the motion detector triggers the camera that records an image of the individual. The trigger in this case is often a pulse or step function in the voltage applied to the dedicated interface port of the camera.
A problem with using most digital cameras and, for that matter, many other devices for event triggered applications is the lack of a dedicated trigger source interface port. Without the dedicated trigger source interface port, these conventional devices cannot be triggered by an external event. Most devices lack a dedicated trigger source interface port in part due to a shortage of real estate on a housing that encloses the device. The real estate shortage makes it difficult or impossible to incorporate a specialized connector to serve as the dedicated trigger source interface port. In practice, extensive and expensive redesign of an existing device is required to introduce event-triggered functionality. This extensive redesign tends to make the device prohibitively expensive and thus relegates the device to a class of highly specialized devices that have dedicated trigger source interface ports and event triggering functionality.
Accordingly it would be advantageous to be able to trigger an electronic device to perform a function or an action by an event external to the device without requiring a dedicated trigger source interface port.